The present invention relates to a silver halide emulsion improved in sensitivity, pressure resistance and processability.
Recently, demand for enhanced sensitivity and image quality of silver halide light sensitive photographic materials has become stronger. In addition, requirements for enhanced photographic performance which is more resistant under external factors such as pressure, processing fluctuations and storage at high temperature and/or high humidity, have been increased.
In response to such requirements, an attempt to enhance photographic performance of a silver halide emulsion by introducing dislocation lines into silver halide grains was made. JP-A 63-220238 and 1-102547 (herein, the term, JP-A means an unexamined published Japanese Patent Application) disclose techniques for improving photographic characteristics through the introduction of dislocation lines. However, as can be seen from the fact that the disclosure of the techniques described above was followed by disclosure of a number of techniques regarding the dislocation lines, further improved technique of dislocation line introduction is still required.
JP-A 3-175440 discloses a technique of allowing dislocation lines to be concentrated at the edge of tabular grains to improve sensitivity and reciprocity law failure characteristics. JP-A 6-27564 discloses a technique of restricting dislocation lines to fringe portions of tabular grains to improve sensitivity and pressure resistance.
Noticeable results of the prior art include improvements of photographic performance by restricting the position of dislocation lines to a specific site. It is supposed by the inventors of the present invention that restriction of dislocation lines to the specific position also limits the position of deteriorating factors produced along with the dislocation lines and these techniques are restrained so as to not produce influences counteracting improvement effects due to the dislocation lines.
The inventors further noted that introduction of iodide ions accompanied formation of a high iodide layer within the grain. As disclosed in JP-A 6-27564, a means for introducing dislocation lines is to introduce iodide ions, forming a gap or misfit of the crystal lattice.
In a technique regarding an iodide content continuously varying layer disclosed in JP-A 5-53232, 9-138473 and 9-211759, improvement of photographic performance such as sensitivity and pressure resistance were accomplished by reducing the gap and/or misfit of the crystal lattice. However, the gap and/or misfit of the crystal lattice resulting from introducing the dislocation in the prior art, i.e. the presence of a layer in which the iodide content is steeply varied, resulted in possibility of counteracting the effects of the iodide content continuously varying layer described above.
It has not been clarified from the prior study whether the crystal lattice gap/misfit as in the prior art is essentially dispensable or not to introduce the dislocation lines. It is supposed that an excessively high iodide layer may be formed.
The presence of the high iodide containing layer with the grain is contemplated to be related to deterioration of photographic performance, such as sensitivity loss due to closely localized lattice defects, lowered pressure resistance and deterioration in processability due to iodide ions released at development.
Supposing that when dislocation lines are formed according to the prior art, a high iodide layer is also concurrently formed, leading to deterioration in photographic performance due to the high iodide layer as well as improved photographic performance due to the dislocation lines, so that effects of the dislocation lines can not be sufficiently displayed, the inventors of the present invention made further study.
Accordingly, it is an object of the present invention to provide a silver halide emulsion with enhanced sensitivity and superior pressure resistance and improved processability.
The above object of the invention can be accomplished by the following constitution:
(1) a silver halide emulsion comprising a dispersing medium and silver halide grains, wherein at least 30% of total grain projected area is accounted for by tabular grains having an aspect ratio of 5 or more and further having dislocation lines of 30 or more per a grain, in a fringe portion of the grain, and the tabular grains each containing silver iodide, the content of which gradually and continuously varies in the direction of from a center to an edge of the grain;
(2) the silver halide emulsion descrined in (1), wherein tabular grains having a silver iodide border account for less than 20% of total grain projected area;
(3) the silver halide emulsion described in (1) or (2), wherein a variation coefficient of grain size distribution is 25% or less and a variation coefficient of grain thickness distribution being 35% or less;
(4) the silver halide emulsion described in any one of (1) to (3), wherein at least 50% of the projected area of total silver halide grains is accounted for by tabular grains having 30 or more dislocation lines per grain, which are localized only in the fringe portion;
(5) the silver halide emulsion described in any one of (1) to (4), wherein at least a part of the tabular grains each contain a reduction sensitization center in the interior of the grain;
(6) the silver halide emulsion described in any one of (1) to (5), wherein at least a part of the tabular grains each contain a polyvalent metal compound in the fringe portion of the grain; and
(7) a silver halide emulsion comprising silver halide grains, wherein at least 50% of total grain projected area is accounted for by tabular grains having an aspect ratio of 5 or more, at least 50% of total grain projected area is accounted for by tabular grains having 30 or more dislocation lines per grain in the fringe portion, and at least 50% of total grain projected area is accounted for by tabular grains, in which the silver iodide content gradually and continuously varies from the grain center portion to the grain edge portion.